Centrifugal fan assemblies generally include a blower wheel that is arranged in a housing and which may be driven by an electric motor. The blower wheel has curved blade fans which draw air in axially, along the axis of rotation of the blower wheels, and discharge air radially outwardly. Such fan assemblies are used in a variety of applications, such as in automotive applications.
In automotive applications it is always an object to minimize the generation of noise, to make the driving of the automotive vehicle as convenient as possible. Furthermore, low noise generation increases the safety of the passengers in the vehicle, because low noise increases the attention of the driver.
The noise of a centrifugal fan assembly is produced mainly by the rotating parts of the centrifugal fan assembly, especially by the blower wheel. Airflow gets into the blower wheel from its top without any rotational motion, then flows into the blade region and is suddenly accelerated to the rotational speed of the blower wheel. This sudden increase of rotational speed results in a separation of the airflow at the leading edge of the fan blades of the blower wheel. This separation results in increased noise, vibration, and harshness as well as in degrading the efficiency of the centrifugal fan.
Another requirement in automotive applications is to minimize the size of the blower for a given flow requirement, or maximize airflow output for a given blower volume. The separation of the airflow also reduces the volume efficiency of the blower unit.
Many attempts have been made to reduce the separation of the airflow at the leading edge of the fan blades, the noise generation, vibration, harshness of a centrifugal fan assembly, and to increase its airflow output for a given volume.
U.S. Pat. No. 5,951,249 A1 discloses a centrifugal fan assembly for an automotive vehicle. The centrifugal fan assembly includes a blower wheel driven by an electric drive and a stationary device which imparts a predetermined amount of spin to a volume of air as the air enters the centrifugal fan assembly. The stationary device is disposed axially with respect to the axis of rotation of the blower wheel and is secured thereto so as not to include any moving parts.
U.S. Pat. No. 5,951,245 discloses a centrifugal blower assembly. The blower assembly includes a centrifugal fan driven by an electric motor and a stationary device which imparts a predetermined amount of spin to a volume of air as the air enters the centrifugal blower assembly. The device is disposed axially with respect to the axis of rotation of the fan and is secured thereto so as not to include any moving parts.
This centrifugal fan assembly reduces the noise generation of the centrifugal fan assembly. However, this centrifugal fan assembly is ineffective since the stationary device cannot create enough rotating velocity in incoming airflow.